Total synthesis of patulolide C and its homo, nor, and iso analogs

Article abstract of DOI:10.1021/jo00077a047

The stereospecific total synthesis of the naturally occurring macrolide patulolide C 19Eb as well as its iso, nor, and homo analogs is described by applying the photoinduced rearrangement of enantiomerically pure epoxy diazomethyl ketones 14 to γ-hydroxy α,β-unsaturated esters 15 as the key step. The required epoxy diazomethyl ketones 14 are obtained by a Sharpless epoxidation of an appropriate allylic alcohol, followed by ruthenium tetraoxide oxidation to an oxiranecarboxylic acid, conversion into amixed anhydride, and treatment with diazomethane. Macrolide 19Zb, which is a geometrical isomer of 19Eb, turned out to be a diastereomer of natural macrolide isopatulolide C, which implies the 4R,11R configuration for this natural material. X-ray diffraction analyses of 19Ea and 19Eb show that there is a considerable difference in spatial arrangement; particularly, the different torsion angles between the carbonyl and olefinic bonds are noteworthy. The conformational behavior of these macrolides is also deduced from the NMR and UV spectra.